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Premise: The use of hybrid breeding systems to increase crop yields has been the cornerstone of modern agriculture and is exemplified in the breeding and improvement of cultivated sunflower (Helianthus annuus). However, it is poorly understood what effect supporting separate breeding pools in such systems, combined with continued selection for yield, may have on leaf ecophysiology and specialized metabolite variation. Methods: We analyzed 288 lines of cultivated H. annuus to examine the genomic basis of several specialized metabolites and agronomically important traits across major heterotic groups. Results: Heterotic group identity supports phenotypic divergences between fertility restoring and cytoplasmic male‐sterility maintainer lines in leaf ecophysiology and specialized metabolism. However, the divergence is not associated with physical linkage to nuclear genes that support current hybrid breeding practices in cultivated H. annuus. Additionally, we identified four genomic regions associated with leaf ecophysiology and specialized metabolism that colocalize with previously identified QTLs for quantitative self‐compatibility traits and with S‐protein homolog (SPH) proteins, a recently discovered family of proteins associated with self‐incompatibility and self/nonself recognition in Papaver rhoeas (common poppy) with suggested conserved downstream mechanisms among eudicots. Conclusions: Further work is necessary to confirm the self‐incompatibility mechanisms in cultivated H. annuus and their relationship to the integrative and polygenic architecture of leaf ecophysiology and specialized metabolism in cultivated sunflower. However, because self‐compatibility is a derived quantitative trait in cultivated H. annuus, trait linkage to divergent phenotypic traits may have partially arisen as a potential unintended consequence of historical breeding practices and selection for yield. [ABSTRACT FROM AUTHOR]

Premise: Plant functional traits are often used to describe the spectra of ecological strategies used by different species. Here, we demonstrate a machine learning approach for identifying the traits that contribute most to interspecific phenotypic divergence in a multivariate trait space. Methods: Descriptive and predictive machine learning approaches were applied to trait data for the genus Helianthus, including random forest and gradient boosting machine classifiers and recursive feature elimination. These approaches were applied at the genus level as well as within each of the three major clades within the genus to examine the variability in the major axes of trait divergence in three independent species radiations. Results: Machine learning models were able to predict species identity from functional traits with high accuracy, and differences in functional trait importance were observed between the genus and clade levels indicating different axes of phenotypic divergence. Conclusions: Applying machine learning approaches to identify divergent traits can provide insights into the predictability or repeatability of evolution through the comparison of parallel diversifications of clades within a genus. These approaches can be implemented in a range of contexts across basic and applied plant science from interspecific divergence to intraspecific variation across time, space, and environmental conditions. [ABSTRACT FROM AUTHOR]

It has been recently proposed that leaf vein length per area (VLA) is the major determinant of leaf mass per area ( MA), and would thereby determine other traits of the leaf economic spectrum (LES), such as photosynthetic rate per mass (A(mass)), nitrogen concentration per mass (N(mass)) and leaf lifespan (LL). In a previous paper we argued that this 'vein origin' hypothesis was supported only by a mathematical model with predestined outcomes, and that we found no support for the 'vein origin' hypothesis in our analyses of compiled data. In contrast to the 'vein origin' hypothesis, empirical evidence indicated that VLA and LMA are independent mechanistically, and VLA (among other vein traits) contributes to a higher photosynthetic rate per area (A(area)), which scales up to driving a higher A(mass), all independently of LMA, N(mass) and LL. In their reply to our paper, Blonder et al. (2014) raised questions about our analysis of their model, but did not address our main point, that the data did not support their hypothesis. In this paper we provide further analysis of an extended data set, which again robustly demonstrates the mechanistic independence of LMA from VLA, and thus does not support the 'vein origin' hypothesis. We also address the four specific points raised by Blonder et al. (2014) regarding our analyses. We additionally show how this debate provides critical guidance for improved modelling of LES traits and other networks of phenotypic traits that determine plant performance under contrasting environments.

Polyploidy, the state of having more than two full sets of chromosomes, has been hypothesized to provide several evolutionary advantages to flowering plants including increased ability to resist pathogens and parasites. However, studies comparing pathogen resistance in conspecific and congeneric diploids and polyploids have produced mixed results. While the supposed relationship between polyploidy and pathogen resistance has been commented on in several narrative reviews, it has never been subjected to a systematic meta‐analysis. We examined the effect of polyploidy on pathogen resistance by synthesizing 214 effect sizes from 128 studies. We find that, overall, there is no consistent effect of polyploidy on pathogen resistance. Subgroup analyses suggest that polyploids perform significantly better than diploids only in resisting hemibiotrophic pathogens, and autopolyploids tend show greater resistance than allopolyploids. This is surprising given the fact that polyploids possess extra allele copies of R‐gene alleles that provide resistance to biotrophic pathogens, and this pattern may indicate that signaling cascades needed to elicit hypersensitive responses are disrupted by polyploidy. Disruption is supported by the observation that, across all pathogens, autopolyploids show significantly greater resistance compared to diploids, whereas allopolyploids do not. This is corroborated by the observation that synthetic autopolyploids perform significantly better than their allopolyploid and established counterparts. Regarding pathogen type, diploids show greater resistance than polyploids to pathogens that are fungi or nematodes. Analyses of publication bias indicate little to no bias, and analyses of heterogeneity indicate that phylogeny explains almost none of the observed heterogeneity. These results underscore the importance of not only systematic review but also the strong degree to which the effects of polyploidy depend on ecological context. [ABSTRACT FROM AUTHOR]

Premise of research. For many questions in evolutionary ecology, it is quite valuable to have an estimate of the span of geologic time over which a group of species has arisen and diversified. This study uses a molecular clock approach to generate a first estimate of key divergences in the evolutionary history of the genus Helianthus, which to date has lacked such an estimate.Methodology. Divergence time analysis was performed with well-resolved phylogenies of Asteraceae and Helianthus in a stepping-stone manner using the RelTime maximum likelihood method with a variety of available macrofossil, fossil pollen, and molecular clock calibrations derived from the literature.Pivotal results. Mean estimates from nine individual calibration scenarios time the divergence of Helianthus from the sister genus Phoebanthus at between 2.47 and 5.41 Ma. Composite calibration incorporating all literature estimates time this divergence at 3.63 Ma, with a 95% confidence interval spanning 0-8.26 Ma. Subsequent diversification within Helianthus is therefore confined to the last few million years.Conclusions. These findings place the origin and diversification of Helianthus into the temporal context of the Pliocene expansion of open habitats across North America and the subsequent vegetation fluctuations of the Pleistocene glacial-interglacial cycles. [ABSTRACT FROM AUTHOR]

Leaf defenses are widely recognized as key adaptations and drivers of plant evolution. Across environmentally diverse habitats, the macroevolution of leaf defenses can be predicted by the univariate trade-off model, which predicts that defenses are functionally redundant and thus trade off, and the resource availability hypothesis, which predicts that defense investment is determined by inherent growth rate and that higher defense will evolve in lower resource environments., Here, we examined the evolution of leaf physical and chemical defenses and secondary metabolites in relation to environmental characteristics and leaf economic strategy across 28 species of Helianthus (the sunflowers)., Using a phylogenetic comparative approach, we found few evolutionary trade-offs among defenses and no evidence for defense syndromes. We also found that leaf defenses are strongly related to leaf economic strategy, with higher defense in more resource-conservative species, although there is little support for the evolution of higher defense in low-resource habitats., A wide variety of physical and chemical defenses predict resistance to different insect herbivores, fungal pathogens, and a parasitic plant, suggesting that most sunflower defenses are not redundant in function and that wild Helianthus represents a rich source of variation for the improvement of crop sunflower. [ABSTRACT FROM AUTHOR]

The leaf economics spectrum (LES) is a prominent ecophysiological paradigm that describes global variation in leaf physiology across plant ecological strategies using a handful of key traits. Nearly a decade ago, Shipley et al. (2006) used structural equation modelling to explore the causal functional relationships among LES traits that give rise to their strong global covariation. They concluded that an unmeasured trait drives LES covariation, sparking efforts to identify the latent physiological trait underlying the 'origin' of the LES. Here, we use newly developed phylogenetic structural equation modelling approaches to reassess these conclusions using both global LES data as well as data collected across scales in the genus Helianthus. For global LES data, accounting for phylogenetic non-independence indicates that no additional unmeasured traits are required to explain LES covariation. Across datasets in Helianthus, trait relationships are highly variable, indicating that global-scale models may poorly describe LES covariation at non-global scales. [ABSTRACT FROM AUTHOR]

The article reports on attempts to develop an unambiguous standardized definition of metal hyperaccumulation in plants. It evaluates the use of artificially amended soils in greenhouse studies and those found to achieve threshold leaf metal concentrations under natural conditions. Proposed guidelines during the study of hyperaccumulation and tolerance in greenhouse studies are also provided.

Plant resource-use traits are generally hypothesized to be adaptively differentiated for populations distributed along resource gradients. Although nutrient limitations are expected to select for resource-conservative strategies, water limitations may select for either resource-conservative or -acquisitive strategies. We test whether population differentiation reflects local adaptation for traits associated with resource-use strategies in a desert annual ( Helianthus anomalus) distributed along a gradient of positively covarying water and nutrient availability., We compared quantitative trait variation ( QST) with neutral genetic differentiation ( FST), in a common garden glasshouse study, for leaf economics spectrum ( LES) and related traits: photosynthesis ( Amass, Aarea), leaf nitrogen (Nmass, Narea), leaf lifetime ( LL), leaf mass per area ( LMA), leaf water content ( LWC), water-use efficiency ( WUE, estimated as δ13C) and days to first flower ( DFF)., QST- FST differences support adaptive differentiation for Amass, Nmass, Narea, LWC and DFF. The trait combinations associated with drier and lower fertility sites represent correlated trait evolution consistent with the more resource-acquisitive end of the LES. There was no evidence for adaptive differentiation for Aarea, LMA and WUE., These results demonstrate that hot dry environments can selectively favor correlated evolution of traits contributing to a resource-acquisitive and earlier reproduction 'escape' strategy, despite lower fertility. [ABSTRACT FROM AUTHOR]

Ceriodaphnia dubia were tested to evaluate the acute and chronic interactive effects of diphenhydramine and sertraline. Observed effects were compared with 2 reference toxicity models, the concentration addition model and the independent action model. Results indicate that the 2 drugs exhibit additive toxicity in C. dubia. In some cases, individually sublethal concentrations of the chemicals resulted in 100% mortality when combined, demonstrating the potentially severe impact of trace environmental contaminants. Environ Toxicol Chem 2013;32:2866-2869. © 2013 SETAC [ABSTRACT FROM AUTHOR]